Rubber composition and process of producing the same



Patented Aug. 27, 1935 UNITED STATES RUBBER PATENH COMPOSITION AND PRODUCING THE SAME Edward Arthur Murphy, Frank Twiss, Wylde G PROCESS OF Erding'ton, and Douglas reen,

England, assignors to Dunlop Rubber Company, Limited, a British corporation 7 No Drawing.

Application, February 11, 1932,,

'Serial No. 592,437. In Great Britain February 12 Claims. (Cl. 106'23) This invention comprises improvements in or relating to the manufacture of rubber compositions, and is particularlyconcernedwith the production from aqueous dispersions of rubber and like material, of dispersions of, granular precipi- 1 tates capable of being consolidated byfiltration into material of continuousuniform texture.

The invention of this application isan im-' provement on application Serial No. 166;612 filed July 8, 1930, the improvement lying in having a large amount of water present during precipitation whereby a fine, granular or fiocoulent precipitate that can, easily be filtered is obtained.

According to the invention the aforesaid dis- ;persions of granular precipitates are produced by a process which comprises efiecting the coagulation of the aqueous dispersions hereinafter specified by precipitating in situ in the presence I of a relatively large quantity of water one or more compounding ingredientsof a nature hereinafter described, by the interaction or double decompositionof one or more waterjsoluble re- .agents having normally no coagulating effects upon the aforesaid dispersionswith one or more Water soluble reagents" an ion orr ions'of which may incidentally possess coagulating influence subsequently added thereto, whereupon the aforesaid dispersions are transformed into dis persions .of granular precipitates,

It is to be understood that the presenceof the relatively large quantity of water .is of extreme importanceuin controlling the size of the precipitate produced, Although the precipitate obtained is sufiiciently coarse to allow filtration a coherent mass is obtained on filtration substantially indistinguishable from that resulting from an ordinary latex film. If desired these dispersions of granular-precipitates can be consolidated by filtration over a filtering surface preferably of suitable form through which passes the major portion 'ofthe water content. I

Furthermore these dispersions of granular precipitates if desired need only be partially concentrated by filtration to form a paste which may be stored and subsequently rediluted for use.

Examples of the water soluble reagents of the first class having normally no coagulating effects upon the dispersions arecarbonates, sulphates, silicates of the alkali metals or of ammonium.

Examples of the water soluble reagents of the second class which interact with the water-soluble reagents of the first class to produce insoluble compounding ingredients are soluble salts of magnesium, aluminium, calcium, barium or zinc;

lents of mixed precipitate; larger-yield of precipitate may be obtained relative to theamount of soluble salt formed.

' trated form.

Concentrates such as are obtained in U. S:

sodium silicate also falls into this class if .the

T OFFICE corresponding reagent in thelfirst class is such as to precipitate silicic acid-e. g. ammonium car.- bonates.

7 By a suitable choice ofthe reagents and con sequent reaction products dispersions of varying consistency can be formed.

If desired the granular precipitates can washed free fromsolublereaction products such as soluble sulphates or chlorides by known means such as filtration and washing priorto their consolidation or concentration;

Numerous substances are capable of being used as compounding ingredients, for example; carbonates of magnesium calcium and zinc may' be two insoluble 'products for example, 'the'ireaction betweenone equivalent of sodium carbonate and one of magnesiumsulphate-.followed by. one equivalent of barium chloride yields only one equivalent of sodium chloride for two'equival- In this manner a The reagents may be a ddedin 'the'for-m of their colloids'such as glue, gu m'acacia in solution" to increase .the fineness of subdivision of the precipitated compounding ingredients.

The rate at which coagulation takes place after the introduction of the water soluble reagents of tion of suitable substances, for example/casein.

- -The emulsions or dispersions oifrubbe'rfor the like comprise those'consisting of rubber, guttav percha,ba1ata"or similar vegetable resins occurring naturally or artificially'obtained. Such artificial aqueous dispersions may include those of coagulated rubber, vulcanized rubber, synthetic rubber, waste or reclaim.

If desired any of the aforementioned dispersions may be used alone or in admixture with one another. Any of the aforesaid dispersions may contain the usual known compounding and. vulaqueous solutions and may contain protective the second class may be controlled byfthe addicanizing ingredients and/or may be-in concen- 2 Patent 1,846,164, or in British Patent No. 219,635 to which may be added any one or more of the usual compounding ingredients may also be used.

The aforesaid vulcanizing and other compounding ingredients Which are added in the form of'their dispersions may be added to; the

aforesaid aqueous emulsions or "dispersions of rubber or the like prior or subsequent to the precipitation-of the granular dispersions.

It is preferable to add the "aforesaid dispersions of the vulcanizing and other compounding ingredients before the precipitation of the granular dispersions. r

In some cases where the precipitate obtained is found to be in a damp powdery or short pastelike condition before consolidation into the com- .pact uniform mass, consolidation can be'l'i'ast ene'd and facilitated by treating'the filter cake obtained with a rubber solvent which may be mixed with a mutual solvent for the water and the rubber solvent employed, as for instance alcohol.

It .is possible accordingto the presentinven- 'tion to produce products having vmechanical properties ranging from those of soft rubber to vulcaniteby the suitablexselection and adjustment of the proportions of the insoluble reaction products. In certain cases it has been found that vulcanizingisunnecessary.

The homogeneous granular precipitates obtained according to this invention are suitable for the manufacture of a large variety of articles such as boot soles, sheet vflooring and treads for tires.

Colloidal magnesium silicate may similarly be for-mediby substituting magnesium sulphate for the aluminum sulphate in the above process.

The following is given-by way of example as to how to produce compact homogeneous rubber sheet from. the aforesaid granular precipitates. A latex having the following composition:-

7 I v v Parts by weight Rubber used inthe. 'form of latex at concentration"; '75 Colloidal aluminum silicate 25 Casein; E

is prepared in the following manner:--

Six parts by Weight of casein are added in the form of 5% aqueous ammoniacal solution to parts of concentrated latex of 60% concentration produced byc'entrifugal-ization. 26 parts of so- 'dium si-licatein theform of 5% solution are stirred into the latex and this is followed by -the additionof 24 parts of aluminium sulphate also in the form of. 5% solution; The total solid content is nowpapproximately 10%.. A slurry like precipitate is obtained which isplaced on a filter base of the desired dimensions and subjected to filtration which may. be aided by external pressureandsuction. After the filter cake has been consolidated to a compact sheet it is placedin a warm air chamber to remove residual moisture.

What we claim is: g

1. A process for the manufacture of compounded homogeneous compositions of rubber which comprises adding to anaqueous dispersion of rubber material a water soluble reagent having normally no coagulative effect upon said dispersion and then adding a reagent to form a water insoluble inert inorganic compounding ingredient by an interaction with said first reagent and having ions which possess coagulating influence upon said dispersion sufficient to coagulate said dispersion, the quantity of water in said resultingmixture being such that the total solids do not exceed ten per cent of said dispersion,

then filteringtheresulting crumb-like coagulate to a compact coherent mass.

'2. A process as claimed in claim 1 wherein the water soluble reag-ents'of the first class added, having normally no coagulating effect upon the aforesaid dispersions are salts of the group consisting of alkali metals or of ammonium.

3. A process as claimed in claim 1 wherein the water soluble reagents ofthe second class added to produce insoluble compounding ingredients are the soluble salts of the group consisting of magnesium; aluminium, calcium, barium or zinc.

4. A process as claimed in claim 1 wherein sodium silicate is-added to the aqueous dispersions aforesaid containing as the reagent in the calcium and zinc.

9. A process as claimed in claim 1 wherein the compounding ingredients produced in :situ are the "silicates of magnesium and zinc.

10. A process as claimed n claim 1 wherein mixtures of precipitates are prepared in such a manner that only one soluble reaction product results from two insoluble products. a 11. A process as claimedin claim 1 wherein the reaction between one equivalent of sodium carbo-nate with one equivalent of magnesium sulp'hate-is followed by one equivalent of barium I chloride resulting thereby in the yield of one equivalent of sodium chloride for two equivalents of :mixedpreci-pitate.

'12. A process as claimed in claim 1 wherein the reagents are added the presence of protective colloids.

EDWARD ARTHUR MURPHY. DOUGLAS TWISS. 

